fix pypa#11847 for sdists

src/pip/_internal/operations/prepare.py

@@ -20,7 +20,6 @@
     InstallationError,
     MetadataInconsistent,
     NetworkConnectionError,
-    PreviousBuildDirError,
     VcsHashUnsupported,
 )
 from pip._internal.index.package_finder import PackageFinder
@@ -47,7 +46,6 @@
     display_path,
     hash_file,
     hide_url,
-    is_installable_dir,
 )
 from pip._internal.utils.temp_dir import TempDirectory
 from pip._internal.utils.unpacking import unpack_file
@@ -305,7 +303,6 @@ def _ensure_link_req_src_dir(
             # We don't need to unpack wheels, so no need for a source
             # directory.
             return
-        assert req.source_dir is None
         if req.link.is_existing_dir():
             # build local directories in-tree
             req.source_dir = req.link.file_path
@@ -318,21 +315,6 @@ def _ensure_link_req_src_dir(
             parallel_builds=parallel_builds,
         )
 
-        # If a checkout exists, it's unwise to keep going.  version
-        # inconsistencies are logged later, but do not fail the
-        # installation.
-        # FIXME: this won't upgrade when there's an existing
-        # package unpacked in `req.source_dir`
-        # TODO: this check is now probably dead code
-        if is_installable_dir(req.source_dir):
-            raise PreviousBuildDirError(
-                "pip can't proceed with requirements '{}' due to a"
-                "pre-existing build directory ({}). This is likely "
-                "due to a previous installation that failed . pip is "
-                "being responsible and not assuming it can delete this. "
-                "Please delete it and try again.".format(req, req.source_dir)
-            )
-
     def _get_linked_req_hashes(self, req: InstallRequirement) -> Hashes:
         # By the time this is called, the requirement's link should have
         # been checked so we can tell what kind of requirements req is
@@ -479,20 +461,24 @@ def _complete_partial_requirements(
         for link, (filepath, _) in batch_download:
             logger.debug("Downloading link %s to %s", link, filepath)
             req = links_to_fully_download[link]
+            # Record the downloaded file path so wheel reqs can extract a Distribution
+            # in .get_dist().
             req.local_file_path = filepath
-            # TODO: This needs fixing for sdists
-            # This is an emergency fix for #11847, which reports that
-            # distributions get downloaded twice when metadata is loaded
-            # from a PEP 658 standalone metadata file. Setting _downloaded
-            # fixes this for wheels, but breaks the sdist case (tests
-            # test_download_metadata). As PyPI is currently only serving
-            # metadata for wheels, this is not an immediate issue.
-            # Fixing the problem properly looks like it will require a
-            # complete refactoring of the `prepare_linked_requirements_more`
-            # logic, and I haven't a clue where to start on that, so for now
-            # I have fixed the issue *just* for wheels.
-            if req.is_wheel:
-                self._downloaded[req.link.url] = filepath
+            # Record that the file is downloaded so we don't do it again in
+            # _prepare_linked_requirement().
+            self._downloaded[req.link.url] = filepath
+
+            # If this is an sdist, we need to unpack it and set the .source_dir
+            # immediately after downloading, as _prepare_linked_requirement() assumes
+            # the req is either not downloaded at all, or both downloaded and
+            # unpacked. The downloading and unpacking is is typically done with
+            # unpack_url(), but we separate the downloading and unpacking steps here in
+            # order to use the BatchDownloader.
+            if not req.is_wheel:
+                hashes = self._get_linked_req_hashes(req)
+                assert filepath == _check_download_dir(req.link, temp_dir, hashes)
+                self._ensure_link_req_src_dir(req, parallel_builds)
+                unpack_file(filepath, req.source_dir)
 
         # This step is necessary to ensure all lazy wheels are processed
         # successfully by the 'download', 'wheel', and 'install' commands.